No Form 6251 on 2021 Return. How to find/figure the "alternative minimum taxable income before exemptions" flagged as error in Smart Check? Should be on Line 4 of 6251.

When completing my 2022 Return, Smart Check asks: 

"Check This Entry
Capital Loss Carryover Worksheet: Line E - AMT should be entered. Enter zero if none
Line E - AMT [_______]"

The referenced form in TurboTax is Schedule D, the box titled "2021 Capital Loss Information Smart Worksheet". Line E reads: "Alternative minimum taxable income before exemptions. (2021 Form 6251, line 4 .....[________]".

This field should have carried over from 2021 Form 6251. It is blank, as there is no Form 6251 on my 2021 Return. How do I arrive at this figure?  -  Thanks